WIP patch Bug 816912 - 3rd party keyboard apps management

1. manage running keyboard layouts in System app
2. list installed keyboard layouts in Settings app
3. use proposed manifest in 3rd party keyboard app
"role": "keyboard",
"launch_path": "/index.html#settings",
"entry_points": {
    "english": {
      "launch_path": "/index.html",
      "description": "English layout",
      "type": ["text", "url", "number"]
    } 
  },